1. Field of the Invention
The present invention relates to a latching or fastening mechanism for securing a pit lid mounting frame to a subsurface chamber for servicing aircraft.
2. Description of the Prior Art
At modern aircraft terminals the servicing of aircraft on the ground is often performed using subsurface pits, which frequently are prefabricated structures. Such aircraft servicing pits are installed at aircraft docking, fueling, and loading areas beneath the surface of the tarmac across which aircraft travel during docking and departure maneuvers. The pits forming subsurface chambers are typically constructed of fiberglass, steel, concrete, or aluminum. These pits are quite often constructed as complete enclosures with surrounding walls, a floor, and an access lid at the top seated within a frame disposed upon the bearing flange at the top of the prefabricated pit. When the lid is closed it lies substantially flush with the surface of the tarmac. Such pits are installed below the surface of loading and refueling aprons at aircraft terminals, remote parking locations, and aircraft maintenance bases.
The purpose of the pits is to allow ground support functions to be carried out from subsurface enclosures. These ground support functions include the provision of fuel, the provision of electricity to the aircraft while it is in the docking area, the provision of air for cooling the aircraft interior, the provision of pressurized air for starting the aircraft engines, and for other aircraft support activities on the ground. The use of subsurface pits eliminates the need for mobile trucks, carts, and other vehicles which are otherwise present in the loading area and which interfere with the arrival and departure of aircraft in the vicinity of a loading gate.
The use of subsurface pits also allows the provision of fuel, power, cooling and pressurized air, and other supplies from a central location. The necessary fluid supplies and electrical power can be generated or stored with a greater efficiency at a central location, as contrasted with mobile generating or supply vehicles.
The pits located below the aircraft terminal area house valves, junction boxes, cooling air terminations, and other terminal equipment that is temporarily connected to an aircraft that has been docked. Umbilical pipes and lines, otherwise housed within the pits, are withdrawn from them through hatches therein and are coupled to a docked aircraft to supply it with fuel, air for cooling the aircraft interior, pressurized air for starting the engines, and electrical power.
The pits are constructed with either hinged or totally removable lids that are set within mounting frames which are positioned atop the prefabricated pits. The pit lid is set within the pit lid mounting frame. The pit lid can be moved relative to the surrounding mounting frame between an open position allowing access to the interior of the pit and a closed position flush with the surfaces of the docking, loading, or refueling areas across which aircraft travel and beneath which the pit is buried.
The pit lid mounting frames are constructed with outer peripheral margins that rest upon peripheral bearing ledges formed at the upper extremities of the prefabricated pits. The peripheral bearing ledges of the prefabricated pits extend laterally outwardly from the mouths which serve as access openings at the tops of the pit enclosures.
Each peripheral bearing ledge typically includes an edge that is turned upwardly to form a surrounding rim. The prefabricated pit thereby forms a peripheral bearing seat to receive the mounting frame for a lid that is hinged or otherwise raised relative to the pit lid mounting frame so as to provide access to the interior of the pit. The pit lid mounting frame is set within the rim of the peripheral bearing ledge. The pit lid mounting frame bears downwardly and is supported by the horizontal surface of the peripheral bearing ledge located therebeneath.
In conventional practice hold down bolts are employed to attach the pit lid mounting frame to the peripheral bearing seat formed at the top of the fiberglass pit. These mounting bolts are installed from the top of the mounting frame and have threaded shanks that extend through internally threaded nuts that are molded into the underside of the structure of the peripheral seat of the prefabricated pit. The bolts are tightened to anchor the pit lid mounting frame to the prefabricated pit in a permanent or semipermanent fashion.
A resilient gasket is normally located in a channel formed in the undersurface of the peripheral margin of the pit lid mounting frame. Tightening of the bolts resiliently compresses the gasket so as to form a watertight seal that prevents rainwater, melted snow, and other surface water from leaking down into the pit enclosure between the edge of the pit lid mounting frame and the peripheral seat upon which it is disposed at the top of the buried pit.
One difficulty with this pit lid mounting frame attachment system is that the hold down bolts can bind up due to exposure to the elements. Once they are removed for any reason they are quite difficult to reinstall. This is because debris can collect in the internally tapped bolt holes. If these bolts are not properly reinstalled or otherwise secured they can become loose on the runway. Runway debris and other foreign objects on an aircraft loading apron can be sucked into the jet engines of an aircraft and create serious damage.